Nuclear power is a new energy which has been paid more and more attention since the first nuclear power plant was built in 1950s. According to statistics, about 441 nuclear power plants have been built in more than 30 countries and regions in the world by the end of 2002, and the generation capacity is about 360 million kilowatts. Now about 40 nuclear power plants are being built and about 60 nuclear power plants are to be built. After completion, the generation capacity will be up to 500 million kilowatts which will take up about 20% of the world's total generating capacity at that time. Uranium or plutonium are generally utilized as nuclear fuel in the nuclear reactor, wherein, the fission chain reaction is conducted in a controlled manner and then fission energy is produced continuously from a special atomic boiler for doing work.
Now a research for joint configuration of nuclear fuel elements/assemblies among the different reactor types of the nuclear power plant is being conducted. As the shape of fuel elements/assemblies varies as the reactor type, during the joint configuration of nuclear fuel elements/assemblies among different reactor types, the fuel elements/assemblies will experience disintegration and recombinant. While among several units of the same reactor type with interchangeable fuel elements/assemblies, the configuration design of the nuclear fuel elements/assemblies in reactor core is relatively independent and lack of unified coordinate optimization.
Under the condition where the configuration design of the nuclear fuel elements/assemblies in reactor core is relatively independent, the fuel elements/assemblies loaded in the first reactor core (it is the core of the first cycle for the reactor type refueling when shutdown) generally are all new fuel elements/assemblies. There three enrichments for the new fuel assemblies are generally used. To take the first reactor core of Daya Bay Nuclear Power Station for example, three enrichments by mass of uranium 235 for the new fuel assemblies are 1.8%, 2.4% and 3.1% respectively.
A method for optimizing the arrangement of the enrichments and quantity of the first reactor core according to the reactivity distribution in the equilibrium cycle is provided in a Chinese published application CN 200510071705.3 of Westinghouse Company, so as to save uranium resources and reach the equilibrium cycle more quickly. The first reactor core configuration design is entirely independent and all the fuel assemblies loaded are still new, except that the range of the enrichments is wider, the types of the new fuel assemblies are more and a low-leakage loading patterns is utilized.
In the method provided in a Japanese published application JP 61-66988A of Toshiba Company, the spent fuel assemblies that can not be used by the operating units any longer are loaded in the first reactor core of the boiling water reactor to replace the new fuel assemblies with natural enrichment, so as to save the natural uranium, manufacturing and the spent fuel disposal cost of the replaced new fuel assemblies. However, this method has serious limitations. For example, in the first reactor core of the pressurized water reactor, the enrichments of the new fuel assemblies in use are generally much higher than that of nature uranium (for example, the smallest enrichment of the new fuel assemblies used in the first reactor core of Daya Bay Nuclear Power Station is 1.8% that is much higher than that of natural uranium with value of 0.71%), and there is no suitable alternative in the first core for the spent fuel assemblies that can not be used any longer by the operating units, resulting in small scope of application and less practical value to other reactor types, and just saving the cost of the new fuel assemblies with natural enrichment for the boiling water reactor which has small effect compared with the cost of the first core. Moreover, the first reactor core configuration design is still completely independent, and just the spent fuel assemblies that can not be used by the operating units any longer is loaded, such that there is no interaction and effect on the reactor core configuration design of the units that have been running